The process by which the body prevents blood loss is referred to as coagulation. Coagulation involves the formation of a blood clot (thrombus) that prevents further blood loss from damaged tissues, blood vessels or organs. The formation of a blood clot is a complicated process involving a first system comprised of cells called platelets that circulate in the blood and serve to form a platelet plug over damaged vessels and a second system based upon the actions of multiple proteins (called clotting factors) that act in concert to produce a fibrin clot. These two systems work in concert to form a clot and disorders in either system can yield disorders that cause either too much or too little clotting.
Platelets serve three primary functions: (1) sticking to the injured blood vessel (a phenomenon called platelet adherence); (2) attaching to other platelets to enlarge the forming plug (a phenomenon called platelet aggregation); and (3) providing support for the processes of the coagulation cascade (molecules on the surface of platelets greatly accelerate several key reactions).
When a break in a blood vessel occurs, substances are exposed that normally are not in direct contact with the blood flow. These substances (primarily collagen and attached multimeric von Willibrand factor) allow the platelets to adhere to the broken surface. Once a platelet adheres to the surface, it releases chemicals that attract additional platelets to the damaged area, referred to as platelet aggregation. These two processes are the first responses to stop bleeding. The protein-based system (the coagulation cascade) serves to stabilize the plug that has formed and further seal up the wound.
The support role of the platelet to the coagulation cascade is provided, in part, by one of the components on the outside of a platelet, called phospholipids, which are required for many of the reactions in the clotting cascade. The goal of the cascade is to form fibrin, which will form a mesh within the platelet aggregate to stabilize the clot. All of the factors have an inactive and active form. Once activated, the factor will serve to activate the next factor in the sequence until fibrin is formed. The coagulation cascade takes place at the site of a break in, e.g., a blood vessel that has the platelet aggregate. Fibrin forms a mesh that, in concert with the platelets, plugs the break in the vessel wall. The fibrin mesh is then further stabilized by additional factors which cross-linkup the clot (much like forming an intricate network of reinforced strands of fibrin).
In the case of trauma-induced bleeding, it is important to understand very quickly the clotting response of a particular individual in order to apply appropriate therapy to treat bleeding and ensure that the trauma is dealt with appropriately. Defective platelet functions, both primary (adhesive, von Willibrand factor interaction) and secondary (fibrin polymer organization and polymerization, integrin function) are recognized as a particularly important contributor in prolonged non compressible bleeding. The development of hemostatic disorders in trauma patients, and associated progression in hemorrhagic and other shock states, can be due to different factors and thus require different therapies.
Currently, thromboelastography (TEG) is the accepted clinical standard for testing the efficiency of whole blood coagulation. As an example, the related U.S. Pat. No. 8,450,078, entitled “Portable Coagulation Monitoring Device and Method of Assessing Coagulation Response” (herein incorporated in its entirety) discloses a portable coagulation monitoring device typically comprising glass plates used to diagnose trauma-related coagulopathies in the field. Further, current methods of introducing blood into, for example, a test cartridge of coagulation monitoring devices may involve measuring the amount of blood required for a test by using a pipette or other capillary device, for example, and then pipetting the required amount of blood into the test cartridge. Blood introduction and the need for clinical staff to pipette blood is a challenge in point-of-care settings and operating room settings where sterility is important.